1. Field of the Invention
This invention relates to an optical diffractor, which in many embodiments, will be used as a multiplexer/demultiplexer.
2. Description of the Prior Art
Optical multiplexing and demultiplexing is normally accomplished by means of a dispersive element, such as a diffraction grating, prism, hologram, etc. One such optical multiplexer/demultiplexer is described in the article "A Six-Channel Wavelength Multiplexer and Demultiplexer For Single Mode Systems" by J. Lipson et al. in Journal of Lightwave Technology, Vol. LT-3, No. 5, Oct. 1985. In the Lipson article, a blazed diffraction grating is utilized for combining and separating various wavelengths of light. Demultiplexing is accomplished by transmitting the multiplexed signal through the grating, which separates the individual wavelengths of light and diffracts each in a slightly different direction. Multiplexing is accomplished by utilizing the same device in reverse; i.e., shining each wavelength through the grating at a predetermined wavelength dependent angle such that all the wavelengths emerge essentially as one single multiplexed beam of light.
This conventional grating, which has been widely utilized in optical communications systems, has several drawbacks. First, some of the incident power is usually lost, because a grating with a period less than half the wavelength of the incident light produces unwanted higher order modes in unwanted directions. Second, due to current manufacturing technology, gratings have limited resolution i.e., wavelengths within 5 Angstroms of each other will not normally be separated. Finally, the grating is typically combined with a lens or reflector to focus the light, and the lens or reflector is difficult to implement in integrated form using, for example, photolithographic techniques.
Several proposals have previously been made in an attempt to overcome the above problems. One optical multiplexer which overcomes the above problems to some extent is described in the article, "New Focusing and Dispersive Planar Component Based on an Optical Phased Array", by M. K. Smit, in Electronic Letters, 1988, Vol. 24, pp. 385-386. In the Smit article, a plurality of optical waveguides are utilized, each of a different length, to construct an optical phased array. The resulting structure acts as a high resolution optical multiplexer. However, due to the fact that there is essentially no mutual coupling among the waveguides, the structure is highly inefficient.